Faculty of Engineering and Built Environment
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Item Multiscale modelling of biogas purification using montmorillonite adsorbent(2024-05) Khuzwayo, Thandeka Ntombifuthi; Ngema, Peterson Thokozani; Ramsuroop, Suresh; Lasich, Madison M.Biogas, a renewable energy source derived from organic materials, offers significant potential for creating sustainable power sources and minimize environmental pollution. However, the presence of contaminants like carbon dioxide (CO2) and hydrogen sulfide (H2S) in biogas can reduce its usefulness and efficiency in a number of applications. To address this issue, this research focuses on the purification of biogas using clay adsorbent. This study investigates the adsorption capacity of clay minerals, such as montmorillonite, in removing CO2 and H2S from biogas. In this study, Grand Canonical Monte Carlo (GCMC) simulations were performed using a self-consistent forcefield to predict adsorption isotherms for methane, carbon dioxide, ethane, and hydrogen sulfide in montmorillonite lattice. The experimental setup involved a Pressure Swing Adsorption (PSA) column, where biogas passes through the adsorbent, leading to the adsorption of impurities while maintaining the methane content, thus enhancing the overall biogas quality. The model was fitted with Langmuir adsorption isotherms for all species at different pressures and ambient temperature, coupled with batch equilibrium approach to model the PSA system. The equilibrium modelling of a pressure swing adsorption system to purify CH4/CO2 feedstock was demonstrated in such that a system can be incorporated into a solar biogas reforming process, targeting purity of 93-96 mol-% methane, which was readily achievable. The modelling of PSA indicate that the system could produce over 96% of methane and a recovery of around 82% at low pressure. The findings suggest that the choice of clay adsorbent and optimization of process parameters can significantly enhance the purification efficiency of biogas via pressure-swing adsorption. The strong selectivity of the montmorillonite adsorbent has affinity to adsorb carbon dioxide and other species at low pressures, even though nitrogen require more pressure to be adsorbed onto the montmorillonite bed.Item Application of synthesized magnetic nanoparticles for biogas production using anaerobic digestion(2023) Amo-Duodu, Gloria; Rathilal, Sudesh; Chollom, Martha NoroSouth Africa is encountering severe challenges in the areas of energy, water, and wastewater management in recent times. This study addresses both water and energy aspects. It aims at using synthesised magnetic nanoparticles (MNPs) on anaerobic digestion (AD) for biogas production from various wastewater sources in South Africa. The study experimented the feasibility of five different synthesized magnetic nanoparticles, magnetite (Fe3O4), copper ferrite (CuFe2O4), nickel ferrite (NiFe2O4), magnesium ferrite (MgFe2O4) and aluminium ferrite (AlFe2O4) on two different wastewater samples (industrial and municipal wastewater) from three sampling sources, Umbilo water works, Umgeni water and a sugar refinery industry. Five research objectives were accessed. The first objective was the synthesis and characterisation of MNPs using scanning electron microscopy/energy dispersive x-ray (SEM/EDX), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. The results showed a surface morphology of facecentred and monoclinic crystal structures with a size less than 20 nm. The nanostructures of ferrimagnetite and magnetite were obtained, and it had an O-H stretching and Fe-O vibration functional groups. The surface area obtained was found to be high for magnetite (Fe3O4) which was 27.597 m2 /g. The second objective was to evaluate the AD performance in terms of water quality and biogas production. This was carried out in two stages. The first was to evaluate the five MNPs with sugar refining wastewater. The second stage was to evaluate the performance of three best performing MNPs on two wastewater samples from Umbilo wastewater. The results for the first stage showed good degradation of organic matter for the bioreactors with MNPs which resulted in a higher yield of biogas and methane as compared to the control as well as good removal of contaminant (chemical oxygen demand (COD), colour and turbidity). Among the five MNPs used, Fe3O4, NiFe2O4 and CuFe2O4 had a contaminant removal efficiency of 60- 70% and a cumulative biogas yield of more than 140 ml/day with more than 85% methane composition, hence these three MNPs were found to be the best performed MNPs. The results obtained from the second stage for the three best performed MNPs indicated a high pollutant removal efficiency of more than 70% for Fe3O4, as well as a biogas yield of more than 1100 ml/day and a methane composition of approximately 98%. The third objective was the evaluation and optimisation of the anaerobic magnetised system for biogas production while the fourth objective involved a comparative study between the performances of magnetised biochemical methane potential (BMP) to non-magnetised biochemical methane potential. From the optimisation study, the predicted results obtained from the BBD-RSM showed an average contaminant removal of 70% and a biogas yield of 522 ml/day at an optimum MNP load of 0.5 g, retention time of 45 days, inoculum load of 500 ml, and a temperature of 35℃ with a desirability of 96% as the optimum conditions. With less than 2% deviation, the confirmatory test demonstrated equal performance at the optimum conditions. Findings from the fourth objective indicated that the BMP system with MF exposure exhibited a contaminant removal rate of over 80% and a biogas generation of 1715 ml/day with a 99.94% methane composition. Overall, the system that included both MF and MNP performed better than the other in terms of biogas yield and colour removal. The final objective was the kinetic study of the anaerobic magnetised system using modified Gompertz and first-order kinetic models. The results obtained from the kinetics showed that the modified Gompertz model described the kinetics and dynamics of the anaerobic magnetised system better than the firstorder kinetic model with a correlation co-efficient (R2 ) over 0.9999 and an error less than 0.0002. Therefore, the possibility of using MNPs, particularly magnetite (Fe3O4), in an AD system for biogas production from wastewater was found to be extremely feasible and without negative environmental consequences. Incorporating both MF and MNP in AD was also beneficial for wastewater treatment because it eliminated the need for post-treatment.Item Wastewater treatment and photo-reduction of CO2 using an integrated magnetized TiO2 anaerobic- photocatalytic system(2022-09-29) Tetteh, Kweinor Emmanuel; Rathilal, SudeshConventionally, the treatment of municipal wastewater involves a sequence of treatment units aimed at reducing pollutants to acceptable discharge levels. Herein wastewater treatment plants in South Africa’s municipalities are being challenged recently due to emerging contaminants (nanomaterials, pesticides, antibiotics, COVID-19 RNA, etc.) that impede their efficiency. This calls for robust technological water solution systems targeted at promoting sustainable water supply and mitigating anthropogenic gas (CO2) emission via biogas production. Against this background, the novel of this study is aimed to develop an integrated AD-AOP (anaerobic digestion – advanced oxidation process) magnetized system to improve wastewater for reuse with biogas production and nanoparticles recoverability benefits. To obtain an optimal balance between robustness and cost-effectiveness of the integrated system, a series of feasibility and engineering works were explored. The first phase involved the synthesis via a co-precipitation technique, characterization, and applicability of the magnetized-photocatalysts (MPCs) for wastewater treatment. Analytically, the scanning electron microscopy and energy dispersive X-ray (SEM/EDX), Fourier transforms infrared spectra, X-ray diffraction (XRD), and Brunauer- Emmett-Teller (BET) techniques showed the tailored MPCs were successfully magnetized. Among the MPCs studied, Fe-TiO2 (with a BET surface area of 62.73 m2 /g) was found as the best with greater potential for above 75% decontamination of the wastewater and methane yield. In the technological design and evaluation, Fe-TiO2 was examined using biochemical methane potential (BMP), biophotocatalytic (BP), biomagnetic (BM), and biophotomagnetic (BPM) systems. Due to the external magnetic field influence on the BPMs, it was found very promising for future adventures. Above all, the novel integrated AD-AOP magnetized system proof of concept showed great potential for recoverability of the MPCs for reuse, reducing the toxicological effects of trace metals (27 elements considered), and improving water and biogas quality. The bioenergy economy of the integrated AD-AOP magnetized system demonstrated net energy being able to subsidize the energy required by the UV-lamp of the AOP system. Conclusively, this finding provides an insight into synthesizing novel MPCs and their applicability for wastewater remediation and biogas production. Also kinetics modeling and response surface methodology (RSM) optimization coupled with artificial neural network (ANN) predictability showed the potential to develop an optimized integrated AD-AOP magnetised system towards the treatment of industrial wastewater, biogas production , and CO2 emission reduction. The prospects necessitate a techno-scientific revolution to upscale the current integrated system into a pilot scale with smart-online monitoring towards improving the wastewater circular economy.Item Anaerobic co-digestion of agricultural biomass with industrial wastewater for biogas production(2021-03-26) Armah, Edward Kwaku; Chetty, Maggie; Deenadayalu, NirmalaWith the increasing demand for clean and affordable energy which is environmentally friendly, the use of renewable energy sources is a way for future energy generation. South Africa, like most countries in the world are over-dependent on the use of fossil fuels, prompting most current researchers to seek an affordable and reliable source of energy which is also,a focal point of the United Nations Sustainable Development Goal 7. In past decades, the process of anaerobic digestion (AD) also referred to as monodigestion, has proven to be efficient with positive environmental benefits for biogas production for the purpose of generating electricity, combined heat and power. However, due to regional shortages, process instability and lower biogas yield, the concept of anaerobic co-digestion (AcoD) emerged to account for these drawbacks. Given the considerable impact that industrial wastewater (WW) could provide nutrients in anaerobic biodigesters, the results of this study could apprise decisionmakers and the government to further implement biogas installations as an alternative energy source. The study aims at optimising the biogas production through AcoD of the agricultural biomasses: sugarcane bagasse (SCB) and corn silage (CS) with industrial WW sourced from Durban, KwaZulu-Natal, South Africa. The study commenced with the characterisation of the biomasses under this study with proximate and ultimate analysis using the Fourier transform infrared spectroscopy (FTIR), the thermo gravimetric analysis (TGA), the scanning electron microscopy (SEM) and the differential scanning calorimetry (DSC). The untreated biomass was subjected to biochemical methane potential (BMP) tests to optimise and predict the biogas potential for the selected biomass. A preliminary run was carried out with the agricultural biomass to determine which of the WW streams would yield the most biogas. Among the four WW streams sourced at this stage, two WW streams; sugar WW (SWW) and dairy WW (DWW) produced the highest volume of biogas in the increasing order; SWW ˃ DWW ˃ brewery WW > municipal WW. Therefore, both SWW and DWW were selected for further process optimisation with each biomass. Using the response surface methodology (RSM), the factors considered were temperature (25-55 °C) and organic loading rate (0.5-1.5 gVS/100mL); and the response was the biogas yield (m3 /kgVS). Maximum biogas yield and methane (CH4) content were found to be 5.0 m3 /kgVS and 79%, respectively, for the AcoD of CS with SWW. This established the association that existed among the set temperatures of the digestion process and the corresponding organic loading rate (OLR) of the AcoD process operating in batch mode. Both CS and SCB have been classified as lignocellulosic and thus, ionic liquid (IL) pretreatment was adapted in this study to ascertain their potential on the biogas yield. Results showed that the maximum biogas yield and CH4 content were found to be 3.9 m3 /kgVS and 87%, respectively, after IL pretreatment using 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) for CS with DWW at 55°C and 1.0 gVS/100mL. The IL pretreatment yielded lower biogas but of higher purity of CH4 than the untreated biomass. Data obtained from the BMP tests for the untreated and pretreated biomasses were tested with the existing kinetic models; first order, dual pooled first order, Chen and Hashimoto and the modified Gompertz. The results showed that for both untreated and pretreated biomass, the modified Gompertz had the best fit amongst the four models tested with coefficient of correlation, R 2 values of 0.997 and 0.979, respectively. Comparatively, the modified Gompertz model could be the preferred model for the study of industrial WW when used as co-substrate during AcoD for biogas production. The study showed that higher biogas production and CH4 contents were observed when CS was employed as a reliable feedstock with maximum volume of the untreated and pretreated feedstock reported at 31 L and 20 L respectively.Item A study of biogas generation from poultry litter and its impurity removal(2019-01) Osagie, Ighodaro; Lazarus, I. J.; Reddy, G.K.; Singh, RamkishoreThis study is focused on the anaerobic digestion of poultry waste to produce biogas. Waste was collected from three different poultry farms (Sekela farm, Emarldene and Parkside poultry industry) in Kwazulu-Natal, South Africa. The aim is to assess energy from poultry waste in Kwazulu-Natal and to enhance the process of biogas production by treating the impurities of sulphur content, moisture and carbon dioxide in the biogas. The objectives are: to determine the energy potential of poultry waste in Kwazulu-Natal region, to increase the energy density of the biogas by the removal of moisture content, incombustible and corrosive gas and to assess techno-economic feasibility of biogas generation from poultry waste. 1 kg of each waste was thoroughly mixed with 3 L of water and loaded into ten digesters with each water bath (thermal conductor) bearing two digesters. The slurry was investigated using water displacement method to determine biogas produced for a period of 21 days and at an average temperature of 30 0C, 31 0C, and 32 0C respectively. Production started on the 3rd day for each digester at different temperatures (30 0C, 31 0C, and 32 0C), and attained maximum value on the 14th and 15th days. The maximum amount of biogas produced was 265.6 ml at a temperature of 32 0C from waste A (Sekela farm). At 32 0C, an optimal biogas yield of 421.6 ml/g VS was observed from Sekela farm (poultry waste A) compared to Emarldene (370.10 ml/g) and Parkside poultry industry (349.10 ml/g) in KwaZulu-Natal. Biogas was collected from the digester with the maximum volume of biogas produced using 100 µʟ gas syringe and was taking to Gas chromatography for characterization. The result showed that it was composed of about 57.71 % methane (CH4), 26.8 % carbon dioxide (CO2), 0.8 % nitrogen (N2), traces of hydrogen sulfide (H2S), fractions of water vapor, and other impurities which the detector was unable to quantify with an energy potential of 0.028 MJ/ml. Purification and Upgrade system was comprised of one column charged with steel wool (iron sponge), and two cylinders charged with pressurized water and silica gel to treat H2S, CO2, and water vapor in the biogas for improvement of its energy density. Biogas was collected from the purified system using gas syringe to the Gas chromatography for characterization and result showed that it is composed of about 84.56 % CH4 and energy potential of 0.046 MJ/ml. The result confirmed that the biogas heating value/energy density was improved/increased using steel wool, pressurized water and silica gel as biogas contaminants removal. Techno-economic studies were carried out to assess the techno-economic feasibility of a small-scale biogas plant using poultry waste in KwaZulu-Natal. A fixed dome digester was selected as the most convenient technology for the community. Result showed that 2,160 kWh per year of energy could be produced from about 4,000 kg of poultry waste and the payback time was eleven years and nine months. It showed that it is techno-economically feasible to use a fixed dome digester for energy generation for domestic usage and is cost-effective. In conclusion, poultry waste as a feedstock is suitable for anaerobic digestion, producing methane which can be used as an energy source and which can be purified to improve its energy potential. Biogas optimization is dependable on: temperature, physio-chemical characteristics of waste, pH and retention time e.g. at same temperature (either 30 0C, 31 0C or 32 0C) and time, waste A production is higher than waste B and C because of its favorable physio-chemical characteristics and pH-value. It is deduced that the energy potential in poultry waste could be determine by treating the waste via anaerobic digestion and the increase in the energy density of the waste is dependable on temperature, pH, retention time and physio-chemical characteristics of the waste.Item Anaerobic co-digestion with industrial wastewater for biomethane production(2020-10-20) Adedeji, Jeremiah; Chetty, MaggieThe increasing demand for energy has led to the utilization of fossil fuels more abundantly as a quick alternative for generation of energy. The use of these sources of energy however as led to the generation of greenhouse gases which tend to cause climate change, thus affecting the ecosystem at large. Thus, there have been the search for alternative sources which cannot be depleted but do generate minimal greenhouse gases. One of such alternate sources is industrial wastewater which have shown to have high concentration of nutrients in the form of organic contents which can be converted by micro-organisms into energy, usually known as biogas, comprising majorly of CH4, CO2 and H2. Another important factor is that industrial wastewaters are a renewable energy source which are continuously generated due to increasing urbanisation and population growth. In this study, the characteristics of three agro-industrial based wastewaters used shows their potential for application in anaerobic co-digestion”. Anaerobic co-digestion method was utilized to harness the synergetic effect of both sewage sludge and agro-industrial wastewater as co-substrate for the generation of biomethane. The result of the effect of varying mix-ratio of the substrates on biomethane production of sugar wastewater and dairy wastewater indicated that mix-ratio of 1:1 for sewage sludge to sugar wastewater operated at 35oC was suitable for optimum generation of biomethane of 1400.99 mL CH4/g COD added and COD reduction of 54%. The model generated using design expert was found to navigate the design space and could perfectly predict the yield of biomethane effectively for the sugar wastewater mix. The biomethane potential tests (BMP) experiment using varying inoculum-substrate ratio (ISR) showed that operating at mesophilic temperature of 25oC with ISR of 1:2 and 2:1 for sugar wastewater and dairy wastewater respectively does increase the methane production within the first three (3) weeks. The kinetic models that best fit the anaerobic co-digestion for sugar wastewater was the first order model while the simplified Gompertz model favoured the dairy wastewater perfectly. The biomethane potential tests indicate significant increase the biomethane production and as well reduction in the volatile solid and chemical oxygen demand (COD) content. In conclusion, both sugar and dairy wastewater can be recommended as co-substrates for anaerobic digestion of sewage sludge for increased and improved biomethane production while simultaneously reducing their COD content at the same time.Item Anaerobic treatment of slaugterhouse wastewater: evaluating operating conditions(WIT Press, 2019-12-11) Chollom, Martha Noro; Rathilal, Sudesh; Swalaha, Feroz Mahomed; Bakare, Babatunde F.; Tetteh, Emmanuel K.The aim of the study was to elucidate the effect of process parameters on the performance of an upflow anaerobic sludge blanket reactor (UASB) that was treating slaughterhouse wastewater. The UASB reactor was operated continuously under mesophilic conditions to evaluate its performance with respect to the removal of organics and, at the same time, monitor biogas production. Organic loading rate (OLR) was varied while keeping the hydraulic retention time (HRT) constant. Chemical oxygen demand (COD) removal efficiency higher than 75% was achieved at an OLR of 9 kg.COD.m-3.d-1, with a HRT of 12 h. Bulking sludge problems were not observed during the reactor operation period. Stability of the treatment process was achieved by the natural buffering of the system due to the produced alkalinity and also due to the characteristics of the wastewaters which was found to be rich in proteins and fatty acids.Item Production of biogas from sugarcane residues(2018) Malunga, Sthembiso Patrick; Isa, Yusuf MakarfiDue to high production costs facing South African sugar manufacturing industries, production of sugar alone may not be profitable. For sugar manufacturing industries to be economically viable, a novel approach research on other value-added potential products is of paramount importance. The aim of this work was to conduct a feasibility study on biogas production from anaerobic digestion (AD) of sugarcane bagasse, molasses and leaves using cow dung as co- substrate. Three sets of 12 independent batch laboratory experiments for each residue were carried out at temperature of 35oC and hydraulic retention time (HRT) of 14 days using 500 ml bottles as digesters. Design-Expert software was used for design of experiment, process optimisation and process modelling. One variable at a time (OVAT) and 2-Dimensional (2-D) graphical analysis methods were used to analyse the effects of cow dung to sugarcane residues (C:SR) feed ratio, media solution pH and digester’s moisture content on biogas volume, methane yield and kinetic constants. The results indicated that the effect of C:SR feed ratio, media solution pH and digester’s moisture content on biogas volume, methane yield, biogas production potential, maximum biogas production rate and lag phase is mutually reliant between all variables, i.e., depended on conditions of other process variables. The optimum biogas volume generated by bagasse, sugarcane leaves, and molasses experiments were found to be 305.87 ml, 522.69 ml and 719.24 ml and respectively. The results showed that the optimum methane yield achieved by bagasse, sugarcane leaves, and molasses experiments were 28.75 ml/gVS, 87.18 ml/gVS, and 85.32 ml/gVS respectively. The overall results showed that sugarcane bagasse, molasses and leaves can be potentially converted into biogas through AD process.Item Optimization of anaerobic co-digestion of sewage sludge using bio-chemical substrates(2018) Madondo, Nhlanganiso Ivan; Chetty, ManimagalayThe anaerobic process is increasingly becoming a subject for many as it reduces greenhouse gas emissions and recovers carbon dioxide energy as methane. Even though these benefits are attainable, proper control and design of the process variables has to be done in order to optimize the system productivity and improve stability. The aim of this research was to optimize methane and biogas yields on the anaerobic co-digestion of sewage sludge using bio-chemical substrates as co-substrates. The first objective was to find the bio-chemical substrate that will generate the highest biogas and methane yields. The anaerobic digestion of these substrates was operated using 6 L digesters at 37.5℃. The substrate which generated the highest biogas and methane yield in the first batch experiment was then used for the second batch test. The objective was to optimize the anaerobic conditions (substrate to inoculum ratio, co-substrate concentration and temperature) in-order to optimize the biogas and methane yields. The second batch test was achieved using the conventional One-Factor-At-A-Time (OFAT) and the Design of Experiment (DOE) methods. Final analysis showed that the bio-chemical substrates could be substrates of interest to biogas generators. Amongst the substrates tested in the first batch experiment glycerol (Oleo-Chemical Product waste) generated the highest methane and biogas yields of 0.71 and 0.93 L. (g volatile solids added)-1, respectively. It was believed that glycerol contains significant amount of other organic substances such as lipids that have higher energy content than the other bio-chemical substrates, thus generating larger biogas and methane yields. Moreover, digestion of sewage sludge alone produced biogas yields of 0.19 L /g VS and 0.33 L/g COD, and methane yields of 0.16 L/g VS and 0.28 L/g COD. Generally, co-digestion yields were higher than digestion yields of sewage alone. Using the OFAT method the results of the second batch test on glycerol demonstrated highest amounts of volatile solids (VS) reduction, chemical oxygen demand (COD) reduction, biogas yield and methane yield of 99.7%, 100%, 0.94 L (g VS added)-1 and 0.75 L (g VS added)-1 at a temperature, substrate to inoculum ratio and glycerol volume of 50℃, 1 (on VS basis) and 10 mL, respectively. Above 22 mL and substrate to inoculum ratio of 1, the process was inhibited. The DOE results suggested that the highest methane and biogas yields were 0.75 and 0.94 L (g VS added)-1, respectively. These results were similar to the OFAT results, thus the DOE software may be used to define the biogas and methane yields equations for glycerol. In conclusion, anaerobic co-digestion of bio-chemical substrates as co-substrates on sewage sludge was successfully applied to optimize methane and biogas yields.